linux-kernel - Re: [PATCH v2 resubmit] sched: Warn on long periods of pending need

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Date:   Mon, 19 Apr 2021 10:08:29 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Don <joshdon@...gle.com>
Cc:     Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...hat.com>,
        linux-kernel@...r.kernel.org, Paul Turner <pjt@...gle.com>
Subject: Re: [PATCH v2 resubmit] sched: Warn on long periods of pending
 need_resched

On Fri, Apr 16, 2021 at 02:29:36PM -0700, Josh Don wrote:
> From: Paul Turner <pjt@...gle.com>
> 
> CPU scheduler marks need_resched flag to signal a schedule() on a
> particular CPU. But, schedule() may not happen immediately in cases
> where the current task is executing in the kernel mode (no
> preemption state) for extended periods of time.
> 
> This patch adds a warn_on if need_resched is pending for more than the
> time specified in sysctl resched_latency_warn_ms. If it goes off, it is
> likely that there is a missing cond_resched() somewhere. Monitoring is
> done via the tick and the accuracy is hence limited to jiffy scale. This
> also means that we won't trigger the warning if the tick is disabled.
> 
> This feature (LATENCY_WARN) is default disabled.
> 
> Signed-off-by: Paul Turner <pjt@...gle.com>
> Signed-off-by: Josh Don <joshdon@...gle.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link: https://lkml.kernel.org/r/20210323035706.572953-1-joshdon@google.com

Thanks!